Publications

Yang, XB; Crews, K (2019). Applicability analysis of MODIS tree cover product in Texas savanna. INTERNATIONAL JOURNAL OF APPLIED EARTH OBSERVATION AND GEOINFORMATION, 81, 186-194.

Abstract
The Moderate Resolution Imaging Spectroradiometer (MODIS) Vegetation Continuous Fields (VCF) tree cover (MOD44B) is an annual product that depicts the fractional coverage of trees on the earth's terrestrial surface at 250m resolution. It has to be noted that the training data of this product is limited to trees above 5 m in height. However, this product has been widely applied in savanna ecosystems where many woody plant species seldom reach 5 m tall. Though the short woody plants in savanna ecosystems could have been reflected in this product due to similar spectral implication as that of tall trees, its applicability has never been rigorously tested. Given so, this study aims to fill this void. It was tested in Texas savanna, which is featured by a wide precipitation gradient and an accompanying woody plant cover gradation. Firstly, we assessed the ability of the MODIS tree cover product in reflecting woody plant cover at pixel level. A per-pixel comparison was conducted between the tree cover values and reference measurement of woody plant cover based on 1-m resolution digital orthophotos. Secondly, we assessed the ability of this tree cover product in reflecting savanna landscape pattern, particularly the potential woody cover pattern over the precipitation gradient in Texas savanna. The MODIS tree cover product based potential woody cover pattern was assessed against the reference pattern of the study area. Thirdly, we assessed the year-to-year consistency of this annual product, under the assumption that tree cover changes very little within one-year period. Reduced major axis regression was conducted between the corresponding tree cover pixels of all successive years from 2000 to 2016. Research results suggest that the MODIS tree cover product has great potential in reflecting woody plant cover at pixel level by empirical calibration. Moreover, this tree cover product demonstrates the ability of revealing the increasing trend of potential woody cover with mean annual precipitation (MAP) across Texas savanna. Furthermore, the lack of temporal consistency is revealed for this annual product. It is worth noting that the potential woody cover pattern endowed by the precipitation gradient in Texas savanna is in a three-segment shape.

DOI:
10.1016/j.jag.2019.05.003

ISSN:
0303-2434